As the technology nodes shrink in some integrated circuit (IC) designs, there has been a desire to replace the typical polysilicon gate electrode with a metal gate electrode to improve device performance with decreased feature size. However, as the gate length and spacing between devices decreases a number of problems arise. For example, it is difficult to select or tune a threshold value for metal-oxide-semiconductor (MOS) devices. It is also difficult to find a metal capable of adequately filling the decreased feature size.
Conventionally techniques use two types of processes are used to tune a threshold voltage. The gap fill metal selection method involves determining a work function metal material which provides a desired threshold voltage. The gap fill metal selection method allows tuning of n-type and p-type MOS devices separately. Gap fill metal selection, however, involves costly experimentation and research into various metals and alloys to find an acceptable material. Even when an acceptable material is found, the material often can not adequately fill the small feature size. The pre-film treatment subjects the gate layer dielectric to a treatment prior to depositing a metal layer. The treatment alters the gate layer dielectric permittivity thereby changing the threshold voltage. However, the pre-film treatment method does not allow a designer to tune n-type and p-type MOS devices separately.